Shirai Kuroko (白井 黒子,Shirai Kuroko?) is a level 4 esper and a student of Tokiwadai Middle School, as well as a member of Judgment. She can usually be found accompanying the third-ranked Level 5 esper Misaka Mikoto — her best friend, partner, and roommate. Though a minor character in Toaru Majutsu no Index, she gets a starring role alongside Mikoto in the Toaru Kagaku no Railgun sidestory.

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The name Shirai Kuroko is quite interesting because it contains both the meanings of "white" and "black".

The family name "Shirai“ (kanji: 白井)can be literally interperated as "white" plus "(water) well"; while the given name "Kuroko" (kanji: 黒子) is more interesting: as a name, it can be interpreted as the stem "Kuro-" (meaning "black") plus the suffix "-ko" - which is commonly seen in Japanese female names (other examples include Saten Ruiko and Kongou Mitsuko); while not used as a name, the term "kuroko" means stagehands in traditional Japanese theatre, who dress all in black.

These literal meanings of Kuroko's name have been referenced several times in the francise:

2) In one clip in Toaru Majutsu no Index-tan Episode 02, a shadowy figure, who dresses all in black, carries Index-tan into the scene. This figure is an apparent reference to "kuroko" (the stagehands). Also, the two tawny ponytails extruding from the two sides of the top of this "kuroko" reminds us of Shirai Kuroko - another apparent pun on her name.

Kuroko is a girl with tawny hair tied into two curly pigtails; the rest of her hair is left to hang as two rows of fringes divided in the middle. Her pigtails are tied in place by a red bow each. Her hair is naturally curly and as such needs to get a straight perm for it.[1]

As per ruling of both Academy City and Judgment, she wears the uniform of Tokiwadai Middle School and the Judgment armband though the latter only during on duty. On her thighs, she secures a pair of black straps where she stores the metal spikes used to secure criminals.

Kuroko can be described as a "girl living in the future". She is used to the world 30 years from now portrayed by Academy City and is thus ignorant to the customs that present-day Japan still practice, like the "love umbrella", which students usually use to link their names to the name of their crush, and the conventional technology outside Academy City.

Aside from being a girl with a modernistic outlook, she can also be blunt when giving her opinions, and this has caused her to be at odds with Uiharu once. Another distinguishing characteristic of Kuroko's is her feelings of romantic love towards Mikoto. In the ongoing Railgun manga her affections appear to be genuine and that she is truly in love with Mikoto. She even allows herself to get severely hurt in order to do what she can to help Mikoto.[2] She is regarded as Mikoto's best friend.

Although usually laid-back and friendly, Kuroko portrays determination and confidence in her own abilities when she encounters enemies, even to those whom she knows is more powerful than herself.[2] To her credit, she is an honorable girl who keeps her word, is kind to children, and shares with Mikoto and Touma the same ironclad sense of justice that makes neither of them ever back down in the face of adversity. According to a particular rumor concerning her and Mikoto: "There's this horrifying teleporter in Judgment who'll tear apart your body and soul if she catches you...and there's another that rules over even that teleporter's body and soul - the strongest Electromaster," although Kuroko had no knowledge of this rumor until a robber she took down told her about it.[3]

Kuroko can be close-minded at times refusing to believe in urban legends without any concrete evidence and even then it will still take some time for Kuroko to accept it. Examples include the boy with the power to make other powers stop working, despite knowing him personally and it was not until when she saw the effects of the Level Upper that she began to suspect it and even than it was only after seeing it a considerable amount of times. Kuroko doesn't seem to like the idea of Gemstones, believing that such a phenomenon couldn't be possible without the Power Curriculum Program.[1]

In her Japanese conversations, Kuroko has the habit of ending the determinative sentences with the auxiliary word "ですの" (desu-no), instead of "です" (desu) in standard Japanese language. This can be seen as her unique label in Toaru francise. For example, Kuroko's catchphrase: " ジャージメントですの！" (pronunciation: Jājimento desu-no! meaning: I am Judgement! or This is Judgement!). This is also shown in her character song Desu no! White & Black.

Kuroko is a first grader from Tokiwadai Middle School. A year before she entered the prestigious school, Kuroko joined Judgment, a special public committee group whose duty is to maintain peace and order in Academy City. The first major case she handled (along with Uiharu Kazari and Konori Mii) was the arrest of a bank robber who can use the esper ability Equal Speed. Despite her young age, she stood up to the much older esper and was beaten up in the process, although a particular bolt of lightning saved her from imminent danger.

In the April of the current year of timeline, Kuroko enrolls into Tokiwadai Middle School.[4] She later falls in love with her, calling her "Onee-sama" (big sister), and then forces her way into her dorm, evicting Mikoto's roommate. The both of them later get punished for this act, but Kuroko stays as her roommate regardless.[5]

She makes her first appearance to Touma in the 3rd volume where she's shocked to see Mikoto is with him, giving him a threat to not lay a finger on her. Later, when Touma decides to investigate the Level 6 Shift Project she meets him again at the dorm where she manages to hide him away from one of the dorm supervisors.[6]

Kuroko is seen hunting down Sherry Cromwell, who had entered the city illegally, and tries to apprehend her but is stopped by her golem. She is saved by Mikoto who also happens to be on the scene.[7] She later appears to help the people stuck in the underground part of the city, teleporting civilians out of the area as Anti-Skill is preparing to fight against Sherry.[8]

Kuroko faces off against Musujime Awaki who has a remnant of the Tree-Diagram, but is out-classed as Awaki proves to be the better teleporter. Awaki teleports a corkscrew into Kuroko's side, as well as several spikes. Kuroko returns the favor back at Awaki during their second encounter, but due to Kuroko being on the move all night without rest, she finds she cannot teleport anymore and ends up being pinned under a pile of furniture. Despite this, she continues to verbally assault Awaki, whose composure and teleporting abilities begin to break down as her psychological state of mind is rattled by Kuroko's taunts and rebuttals. Kuroko eventually manages to summon enough strength to overcome the the furniture pinning her down and stand up to face her now-panicking opponent. Using a lamp as an improvised weapon, Kuroko charges at Awaki; the latter reacts by pulling out a gun and shooting her in the torso. Awaki, who is by then in the grip of a mental breakdown, decides to crush Kuroko by collapsing the upper floors of the building onto her. Kuroko, who is almost completely incapacitated and barely conscious, only just manages to be saved by Mikoto (who used her railgun to tear open an entry point into the building) and Touma (who grabbed Kuroko and then used his Imagine Breaker to stop the teleport). Kuroko is then taken to the hospital.

At the hospital, Touma visits to see how she is healing up, and accidentally walks in when Kuroko is changing clothes. He is rewarded with a slap from Kuroko.[2] Later Kuroko jokes that Touma likes girls who are less aggressive, but after seeing Mikoto take the suggestion seriously, she gets upset thinking Mikoto really has fallen in love with Touma. Kuroko vows silently to herself to get stronger herself so that Mikoto will rely on her more, and not be a burden after the 'Tree Diagram Remnant' incident.

Kuroko is unable to participate in the Daihasei festival due to her injuries from the Remnants incident, and is in a wheelchair during the course of events, escorted by Uiharu Kazari. She is seen to cheer up for Mikoto who is taking part in a competition between schools. After seeing Mikoto taking care of Touma on a public TV screen, she vows to kill him for taking advantage of Mikoto and stealing her rightful place.

Although mentioned several times before, Kuroko reappears again in the novels at last and debuts silently in Shinyaku Toaru Majutsu no Index. She appears with Konori Mii across the road where Uiharu Kazari is. As a member of Judgment, it is her duty to aid Anti-Skill during the Ichihanaransai. She witnesses Mii calling out to Aogami Pierce for questioning, deeming him to be a suspicious person. Kuroko asks her on why they couldn't just throw him into a cell, as there are cases and mysterious reports that are needlessly driving down their efficiency, especially about rampaging Rhinoceros beetles. Mii says not to take her frustration on Aogami, to which she then asks for his belongings to check them.[9]

That was the 43rd time he has been questioned by authorities that year.[9]

In the second recreation of the world by Othinus, known as the Version_Beta world in-text, where another "Kamijou Touma" exists living Touma's life. In this world eerily similar to Touma's world, Kuroko is only referenced by Mikoto to be busy when she is forced to confront the sender of the junk mail to Tokiwadai's dormitory, a task that is usually handled by Kuroko according to her.[10]

In the final recreation of the world by Othinus created specifically to break Touma's spirit, known as the Version_Omega world in-text, where several characters from the original world have been "saved" or have not experienced great tragedy, Kuroko, Kazari, and Ruiko are in the festival where Touma is after his spirit has already been broken, trying to decide how he should have himself killed. Here, they are all aware of the existence of clones. Kuroko complains on how there are too many people in the festival and wonders where Mikoto had ran off to. Kazari comments on how it would be impossible to find her in the festival with all the people who look like her. Ruiko then comments on how she just remembered that Meigo Arisa may be coming in secret, referring to her "perfect mode" after becoming one with Shutaura Sequenzia. Kazari comments on how she saw the doll-like child president wandering around earlier, as such Arisa may be around.[11]

Kuroko is seen doing her duty as a member of Judgment detaining espers whose powers were enhanced by Level Upper. Due to injuries she sustained from fighting Level Upper users, she couldn't partake in rescuing Uiharu from Kiyama Harumi or help Mikoto fight the AIM Burst.

Kuroko is first seen in this arc with Mikoto and Ruiko helping Uiharu's new roomate move in. Later they go to a festival where a Poltergeist happens, and after observing Erii's odd behavior right before the incident and some investigation, she begins to suspect that Erii is the one responsible, which strains her relationship with Uiharu.[14][15] When the head of MAR, Therestina Kihara Lifeline's true intention for Erii and Kiyama's students was discovered, she slapped Uiharu to snap her out of her emotional breakdown. Later, she and Mitsuko joined forces to stall the MAR powered suits, then came to Mikoto's aid against Therestina herself. At the lab, they are again confronted by Therestina, only this time she Capacity Down to disable them, except for Saten as she was a level zero and thus unaffected by Capacity Down, and went ahead to disable it, an act that earned her Kuroko's respect.

Although showing rarely, she is the one who opens up the question to Mikoto on what would happen if she were to meet a clone of hers, to which Mikoto gives an answer that she will soon regret. Throughout the story arc, she becomes concerned as to what Mikoto is holding and laments on how Mikoto cannot trust her enough to tell. Kuroko is forced to lie to and deceive their dorm manager for Mikoto's sake as she begins her one-man mission to take down the Level 6 Shift Project.

Later, after Mikoto believes she has shut down the Level 6 Shift Project for good, Kuroko calls Kazari and Ruiko to determine what they should do with the current situation with Mikoto. Ruiko concludes that since Mikoto goes out every night and comes home tired, it can only mean that there is a boy involved, much to Kuroko's disbelief. After an alarm goes off in Vending Machine 7116, she immediately concludes it is Mikoto and proceeds to go investigate alone. She later finds Mikoto with Kamijou Touma leading to the now classic scene of their meeting. Regardless of her horror of Mikoto meeting with Touma, she is relieved that she has returned to her old self.

This is however short-lived, as Mikoto later discovers that the Level 6 Shift Project persists. Kuroko sees through Mikoto's change of behavior and suspects that Touma might have something to do with it, but is then asked by Mikoto a hypothetical question on what Kuroko would do if Mikoto were to do something irreversible to Academy City, to which Kuroko says that she will do her duty even if it is her Onee-sama. Kuroko's words relieves Mikoto but it doesn't help Kuroko's worry. Finally, as Mikoto goes off to destroy Tree Diagram to stop the aforementioned project, Kuroko lies alone in Mikoto's bed worrying about her. She recalls on how Mikoto acts normally when referencing "that idiot" (Touma), and wishes for him to come and do something. Her wish is seemingly granted, leading to their second meeting in the Sisters Arc.

As the Level 6 Shift Project is ended by Touma and the Sisters, Kuroko tracks down Mikoto on a bridge, whom has just met Touma but is unable to give the cookies she baked for him. Kuroko is surprised by Mikoto's reaction after she hears Touma say her name for the first time, saying that it is an expression she has never seen on her before.

Kuroko plays a supporting role in the arc. As Mikoto returns back to normal after the events of the Sisters Arc, Kuroko welcomes her back with open arms. When Mikoto once again starts acting secretive, Kuroko is fine with it, believing that Mikoto will be back, and supporting in her endeavors. However, when she opens up to them that she needs their aid in helping Febrie from the dark side of Academy City, Kuroko jumps at the call to help her.[16] She is the one who rescues Mikoto from the office building STUDY stuck her in after she was captured, using Kazari as the one who tracks the nanodevice embedded inside Mikoto, and Ruiko as the lookout. She easily defeats the security robots stationed there.[17]

Kuroko during the Silent Party.

Kuroko gets involved when the group decides to take on STUDY and the Silent Party without any help at all from Anti-Skill for the sake of Febrie and Janie, Febrie's sister. She stands as a sole guardian of one of the Academy City Research Exhibition Assembly venue entrances, and faces off against several of the 20,000 plus STUDY Powered Suits controlled by Diffusion Ghost. After being joined by other Judgment members rallied by Yanagisako Aomi, she is shocked after all of them copy her famous catchphrase. She then does battle against the Powered Suits, and uses the javelins from Tokiwadai, easily defeating a Powered Suit with a single hit. She also uses her ability to rescue Judgment members who are in trouble.[18]

Kuroko is part of the little conference held after Mikoto defeats Aritomi Haruki, STUDY's leader, who has launched the AIM bomb. Here, she is the one who is to go with Mikoto and teleport her back after she has used the Ekaterina II S to destroy the AIM bomb. As they strap themselves in the mecha while waiting for launch, Mikoto apologizes to Kuroko for involving her, to which she replies that she doesn't mind for she is finally fighting side by side with Mikoto. With that, they are launched into space by Mitsuko's Aero Hand. Kuroko becomes visibly sick upon arriving in the upper atmosphere, but manages to teleport away as Mikoto begins to do her part. Kuroko teleports an exhausted Mikoto back to earth after she destroyed the AIM bomb. She is later seen asleep near Mikoto along with Kazari, Ruiko, Mitsuko, Kinuho, and Maaya in the grounds of the Academic Assembly venue, most likely tired, as the Assembly begins in earnest.[18]

As Janie and Febrie are in a Kongou Airlines runway, preparing to leave to the outside for body readjusments, Kuroko gives her the four leaf clover she found those many days ago for good luck. And thus, the fellowship, though bound by friendship and love, part ways.[18]

Kuroko, Ruiko, and Kazari appear right before Mikoto's competition in the three-legged race with her partner Kongou Mitsuko. Ruiko tells Kazari of a substance known as Shadow Metal that is formed by the clashing of multiple espers, which can be sold for a large sum of money. Kuroko then appears right after, angry at Ruiko for spreading rumors again, to which forces her to distract and stay her anger by pointing out that Mikoto's competition is about to begin.[19]

After the race, Kuroko is not present with the others as they meet Misaka Misuzu, explainiing Kuroko's suprise in Toaru Majutsu no Index when she meets her later in the afternoon of the first day of the Daihaseisai. Kuroko doesn't reappear until after much later during the lunch break. She returns with Misaka Mikoto back to Judgment 177 Branch Office as the former have a bit of time before her next event. At the time Kazari is communicating with Ruiko as she is in Kirigaoka Girls' Academy grounds in School District 18 looking for Shadow Metal. Immediately after, Ruiko is attacked by men in hazmat suits. Concerned, Mikoto asks Kazari what is going on, to which he explains that Ruiko is being attacked by someone on the other line. Hearing this, Kuroko and Mikoto mobilized after Kazari says that Ruiko is in Kirigaoka Girls' Academy grounds in School District 18. Kazari is left behind for a backup as they might need to contact Anti-Skill. Arriving there, Kuroko notices them, but Mikoto, seeing Ruiko being held down angers Mikoto and attacks them. Mikoto and Ruiko later prostrate themselves in apology to them after it is revealed that they are the one who clean the grounds after an event to prevent the DNA traces of espers from being stolen by outsiders. Seeing Ruiko as a trespasser in the grounds, it was only natural for them to apprehend her. They are later let go by them. Kuroko says that the rumors of Shadow Metal spread because of the fact that the grounds were heavily guarded to prevent DNA maps from being stolen, and berates Ruiko for being carried away by a baseless rumor, as well as Mikoto for the attack.[20]

The others later arrive back in the office, and much to Kuroko and Mikoto's chagrin, Ruiko then immediately asks Kazari if she had found any new information. Kazari then says that she has done some searching herself but couldn't find anything.[20] Little did they know that Misaki paid Kazari a visit and have read her memories that she and the others are Mikoto's friends,[21] modified her memories so she forgets about the website and have her erase the data of it from her computer,[22] and have programmed her to lead her and her friends to her on the next day.[21] Kuroko is with Mikoto during the Night Parade where Mikoto becomes as excited as a child when the Gekota float comes by.[20]

The next day, she is with Kazari and Ruiko for their patrols, completely unaware that Misaki has begun her move against Mikoto. Kazari, as programmed by Misaki, takes Ruiko and Kuroko away from their proper patrol route. Kuroko realizes that they are in the wrong route, which surprises Kazari truly believed she was going the right way. Then, Keitz appears behind them, pretending to be an outsider in need as a distraction. Misaki later comes out of an alley as they are distracted and uses her powers to freeze their movements, preventing Kuroko from using her powers, and later erases their memories of Mikoto.[21] As Mikoto tries to escape Misaki's clique, she notices Kuroko, Kazari, and Ruiko walk along by. She is relieved and comes towards them, but much to her horror, discovers that they too have been brainwashed by Misaki.[21] Mikoto is greatly angered by this effrontery, but is unable to do anything even if she tries to convince them that she is truly their friend. Moreover, Mikoto has another event to partake in.[23]

Mitsuko, fresh out of her latest event, later meets up with Kinuho and Maaya and later stumble upon Kuroko and the others. Kuroko later airs her frustration on Mikoto coming up to her, making an accusation, and then asking them if they were joking. This surprises Mitsuko, Kinuho, and Maaya, wondering if Kuroko and Mikoto had a fight. Back with Kuroko and the others, she wonders on how Ruiko and Kazari knew Mitsuko. They point out to her that they met when they were visiting Kuroko in the hospital, though this confuses Kuroko as she is not close with Mitsuko. The others can only conclude that there was a mutual acquaintance but cannot remember who.[23]

The girls go their separate ways for the moment, with Kuroko likely doing her Judgment duties independent of Kazari's help. Kuroko doesn't appear until after Ruiko becomes involved with the incident with Kongou Mitsuko and Baba Yoshio and discovers that she has Mikoto's number in her cellphone. Seeing this, Ruiko later contacts Kuroko and would talk to her about on how they are friends with Misaka Mikoto, much to her disbelief. Kuroko questions Ruiko's theory on Shokuhou Misaki manipulating their memories. Kuroko then asks why she didn't contact Kazari. Ruiko, who has already suspected that Kazari has been the first one to have been brainwashed by Misaki, says that she is hesitant in telling her. In the end, she tries to call Mikoto as she has a message for her.[24]

Mikoto later receives a call from Ruiko with Kuroko eavesdropping on the conversation as Mikoto continues to search for clues regarding her "sister". After Ruiko introduces herself, she tells Mikoto about the information they had gathered from Misaka 10032's cat. Mikoto says that she has no clue what that girl with the man from the cat's memories, who she says is likely Misaki, is talking about. Just then, Ruiko says that there is something that she is knowledgeable about that came about in the conversation that the cat has heard, and that she also wants to know whether she and Ruiko know each other. Ruiko requests that they should meet each other, to which Mikoto says her location and it is in School District 15, which Ruiko notes is quite close. Ruiko asks for Mikoto to stay there as she'll ask Kuroko to teleport her to where she is, much to Kuroko's frustration. After Mikoto discover that Kuroko is with Ruiko, Kouzaku Mitori's Liquid Shadow dummy approaches her, telling her that she wants her to tell her something. Mikoto, already suspicious, says that she is quite busy and has no time to talk to strangers, but she'll make an exception to those who are connected with the guy (Baba Yoshio) who hurt her friend. Mitori is unperturbed and shows that she has Kazari hostage.[24]

Ruiko then contacts Kazari to know what's going on, to which Mikoto detects using her powers. As Kazari didn't answer, Kuroko quickly teleports to where Mikoto is and hides on a rooftop.[22] She later sees the negotiation between Mikoto and Mitori breakdown, ending with Mikoto declaring that she will definitely save Uiharu Kazari, which Kuroko notices that it may be directed towards her. Mitori laughs and asks if Mikoto's mother was expendable. As she remarked how cruel that was, Mikoto attracts some pipes with magnetism to pull Kazari away while attracting her phone to block the knife, before moving in and attacking with electricity.[22]

Seeing that the negotiation had failed, Mitori attempts to carry through with her threat, saying she wouldn't like it to end with Mikoto underestimating her and telling Misuzu to resent Mikoto for abandoning her. At that moment, Shirai Kuroko teleports in and smashes her wheelchair down at her. Jumping out of the way, Mitori throws a knife at Kuroko, who evades it. She then escapes as Kuroko was teleporting Misuzu to safety. Kuroko wanted to apprehend her but knows that keeping civilians save is the greater priority. She later takes Misuzu and hands her over to Mikoto, thinking that she can just apprehend and interrogate the one that held Kazari hostage. After Mitori escapes, she has her Liquid Shadow puppet to attack Kuroko as she moves in closer, though she misses. Kuroko tries to attack with her darts though they simply right through the puppet. As the puppet comes closer, Mikoto tells Kuroko to take Kazari and Misuzu to safety, though before she can do so, the puppet merely points towards her with a smirk before it dissolves as Mitori moves out of range.[22]

After the conflict, Kuroko demands from Mikoto an explanation. Mikoto says that she didn't know who was that either, to which Kuroko explains that she wants to know why Mikoto acted like she knew she was there, saying that the line about Mikoto saving Kazari was meant for her. Here, Mikoto explains that she noticed Ruiko calling Kazari after she hung up through the electromagnetic waves, likely to see what had happened. As she has told them where she was, she expected Kuroko to come over as she can teleport and that she would be nearby. Mikoto thanks Kuroko for letting her save Kazari, to which Kuroko says that Kazari is part of Judgment and that it is only natural to prioritize visitors. Kuroko references that Mikoto left her mother's life in the hands of a stranger, to which Mikoto notes on her mother would be mad if she chose her instead of friend. Moreover, she tells Kuroko that she trusted her to protect her mother. Hearing this, Kuroko blushes and tries to shake it off, but it aggravates her injuries. Mikoto apologizes for letting her fight when she was injured and tries to help her walk, much to her embarrassment.[22]

They later return to Judgment 177 Branch Office, and later lets Kazari and Misuzu have some medicine and some sleep. With that they discuss about the situation at hand. Mikoto confirms to Ruiko that the girl that Misaka 10032's cat saw is definitely Shokuhou Misaki and has abducted her "sister. Ruiko then mentions Auribus oculi fideliores sunt, an urban legend website she knows of. Kuroko questions why Misaki would be interested in that, to which Ruiko says that the site not only gathers information about urban legends but has people go out and verify it. She relates on how yesterday after the midday break, the time after Mikoto's sister was abducted, she was out looking for Shadow Metal and had Kazari look up the site. When she returned Kazari says that she couldn't find it, prompting her to find it on her own only to find that the website got buried by a bunch of dummy sites. Ruiko explains that once something is on the Internet it can never fully be deleted. She says that somehow someone is trying to hide the website by making dummy pages that will have higher spots in the search results. Mikoto can only assume that there must be something in that website that someone doesn't want to see. Kuroko then mentions that Kazari would have noticed something and had the skills to search for the cause of it. Mikoto conjectures that someone had detected her actions and attacked her. She imagines Misaki doing it, manipulating Kazari to delete the data and then searching her memories to find that she is friends with Mikoto. Ruiko says that they have to force the clues together to reach the conclusion, but says that there still must be something remaining in the computer that could help them.[22]

Using her powers, Mikoto recovers the deleted data. She finds a picture of Misaki from the website, confirming her suspicions. Mikoto asks Kuroko if she can identify where she is, to which Kuroko says that it might be School District 2 due to the building in the background. Before Mikoto can run off to confront Misaki herself,[25] Ruiko asks Mikoto if their memories were truly altered, and that if they are truly their friends, to which Mikoto says that she will drag Misaki here and that they should wait.[26]

Ruiko becomes restless at waiting, to which Kuroko says that Mikoto was the one who told them to wait and that she shouldn't worry. Moreover, she is still honestly unbelieving that they had their memories erased. Ruiko comments on how having her memories of her friends erased would be bad and that she'd hate it. She later finds Kuroko looking up a list of girls in the Bank, to which Kuroko says that she saw the one that attacked Kazari, and that she had been looking for her in the Bank based on her powers, as well as her sending the liquid metal and knife for forensic analysis. Ruiko becomes excited over this, to which Kuroko says that she is merely acting as a member of Judgment, and that she cannot hand over the investigation to a normal person. She then says, with much embarrassment, that she can make an exception as the situation is urgent and that sharing information would be beneficial. Ruiko then has a smug look on her face, much to Kuroko's consternation as Ruiko begins helping her.[26]

Ruiko later discusses her hypothesis regarding Kazari being controlled by Misaki since yesterday, leading to them to conclude that is the reason why Kazari took them to the wrong patrol route. Ruiko then says that they should keep it a secret from Kazari, saying that she is the type that to feel responsible when no one is to blame. Just then, Kazari has woken up from the infirmary opens the door and asks them to tell her exactly what they are talking about, to which Kuroko agrees, much to Ruiko's shock. She however, says that Kazari should first make some tea. Kuroko whispers to her that she admires that she is protecting Kazari, she says that she isn't that weak to have that break her. After being briefed about it, Kazari is dismayed for being manipulated. Kuroko however says that after their break they should restart their investigation, and asks Kazari if she can look through the Bank for anyone suspicious. Kazari asks if she is sure that she can trust her, to which Kuroko says that they do not have time to have a detailed examination as they need her skills now. She then tells her that if she is really worried, then she can do her work in front of them. Kazari goes right to it, impressing Ruiko.[27]

As they investigate liquid metal, Ruiko notes that only two companies that have developed liquid metal have survived. Kuroko says that the companies have no record of loss or theft, which opens up the possibility that someone inside the company is helping the esper using liquid metal (Mitori). Just then, Kazari has finished the search according to Kuroko's specifications and they discover that the name of their attacker is Kouzaku Mitori. Finding information about her, Kazari says that Mitori is in the Reformatory for an attempted terrorist attack 14 months ago. Ruiko asks if she escaped, to which Kazari says that if she did, then Judgment should've been notified. Kazari asks again if Mitori truly was the culprit, to which she confirms. Regardless however, Kuroko wants to double-check and says she wants to go to the Bank's control center. Kazari then asks what Ruiko would seeing as she will likely not be allowed there as she is not a member of Judgment. Ruiko says that she will pass and asks about Misuzu, to which Kuroko says that she has explained the situation to Konori Mii, their senpai. She says that Mikoto wished for Misuzu to be told that she collapsed of heatstroke and that she will be kept in the office for protection under the guise of getting a new ID issued.[27]

With that they all leave the office, with Kuroko and Kazari going to the Bank's control center. When they arrive, Kuroko discovers that Mitori has been dead for at least two months due to heart failure. Kuroko wonders if she was wrong in her assumption, but then finds something odd. She discovers that her body was incenerated immediately after she was found instead of getting an autopsy. Then, the a minder in the Bank comes up to them and says that Mitori may not have one. She explains that they might have something to hide and that they destroyed her body, evidence, before the true cause of her death could be found. She also says that Mitori might not even be dead. When asked, the minder says that there is a rumor about the Reformatory, and on how student suddenly disappear for some reason. When the guards report it they are waved off and ignored and it is always high level espers or excellent students who disappear. She says that Academy City makes a deal with the esper or student and releases them in secret and then fake their deaths as it is far more convenient, though she says it is just a rumor.[28]

They are later contacted by Saten Ruiko after getting information from Xochitl regarding the situation Mikoto is in. Kuroko then teleports to School District 2 as the Level 6 Shift attempt on Misaka Mikoto takes place.

Kuroko arrives at the rooftop of the building which holds Exterior, just in time to save help Misaki from being abducted by Mitori and her Liquid Shadow puppet. As Kuroko declares her intention to arrest and question everyone present, especially Mitori for falsifying of the Bank's data, Mitori attacks with her puppet. Kuroko evades her attack and on Misaki's request, teleports Keitz and Misaka 10032. Mitori attempts to attack the two but Kuroko teleports herself and Misaki away into the building, who knows that the puppet is at the maximum control range she has for maintaining control over both the puppets and Mikoto. Inside the facility, Misaki uses her powers on Kuroko to quickly brief Kuroko on what was going on, that Mitori is not a mere bodyguard but a guide for Mikoto's psyche, the likely place where she is hiding through the range of her control of her puppets, as well as the fact that they can stop Mikoto if she stops Mitori.[29]

As the battles for Misaka Mikoto goes on in other places, Kuroko meanwhile teleports from building to building trying to find Mitori. She recalls Misaki's informing her, in that Mental Out isn't very effective on Mikoto, and as such the Liquid Shadow puppet cannot give Mikoto orders. This leads her to conclude that Mitori can only guide Mikoto's psyche if she is nearby. However, with such a high concentration of research facilities near where Mikoto is, Kuroko contacts Kazari and asks her to check every camera within 800 meters of School District 2's Judgment building. She tells Kazari to see if she can find Mitori on one of the cameras as well as a list points the cameras do not cover. Kazari asks Kuroko if she needs backup, to which Kuroko says they do not have time.[30]

As Kuroko teleports into one of the buildings, Mitori has her puppet slice through a door to attack her. Kuroko then proceeds to engage the puppet in combat.[30] As she battles, she finds out where Mitori puts the camera on her Liquid Shadow puppet so she can see, which is on her neck. She attacks it with her darts, disabling Mitori's secondary senses, and forcing her to use echolocation to grasp the situation, Mitori's primary sense for her puppet. She then uses a small device to deafen her ability to echolocate. Kuroko then teleports away as the puppet is preoccupied, trying to search for Mitori. However, the facility is so vast, she requires the aid of a clue. Back in Judgment 177 Branch Office, Ruiko manages to find Mitori in one of the cameras. Kazari contacts Kuroko, telling her of Mitori's moving into an alleyway three minutes ago, though she can't tell what building she's in as she hasn't been seen in the other cameras. Kuroko then rushes toward the likely location of Mitori.[31]Kuroko asks if they're sure Mitori hasn't been seen in any other camera, to which Ruiko confirms. Kuroko notes that Mitori would show up in the cameras if she moved into another building. Seeing this, Kuroko manages to pinpoint the building where Mitori is likely hiding in. She orders Kazari and Ruiko to turn all nearby movable cameras toward the building as she teleports in.[31]

Back with the puppet, Mitori is able to pierce the device, but then realizes that the security cameras likely gave her location away. She then has her puppet slice and enter a sewer pipe to head to where Kuroko is going.[31] Kazari notices this as well, and reports it to Kuroko, confirming to her that the place where Kuroko is in is where Mitori is hiding. Mitori, turns her attention to Kuroko, and uses the cameras of the Homing Cameras that is used for Daihaseisai events to target her. Mitori observers the battle directly during the puppet's confrontation with Kuroko in the building. After Kuroko uses the anti-listening device on her puppet again, Mitori uses the puppet to attack her, though could only spread her attack as she could not tell how high up Kuroko is. Despite being hit on the side and on the arm, Kuroko teleports away and applies a small a balm on her injuries. While doing so, she believes that Mitori is in the building based on the puppet's actions and that she is in the upper floors. After treating her wounds, Kuroko pursues Mitori from below, though notes that she may be overlooking something.[31]

Meanwhile, back in Judgment 177 Branch Office, Ruiko and Kazari becomes worried of Kuroko's injuries. Kazari, as she watches the cameras, later catches the Daihaseisai Homing Cameras surrounding the building where Kuroko is in despite being no events. Kazari researches that Anti-Skill apparently used them to see if anyone has yet to be evacuated but notes on how the powerful electromagnetic waves there are too powerful for the cameras to approach. Ruiko then gets the idea in having them use the cameras to aid Kuroko, leading Kazari to eureka moment. She asks Ruiko how long the cameras were there, to which she says that they have been there since Kuroko entered the building. Kazari then reports this to Kuroko, giving to her the possibility that Mitori is not inside the building but somewhere else.[31]

With this new knowledge, Kuroko continues her pursuit of Mitori inside the building. Kuroko finds the last blindspot of the building, only to find that she isn't there. Kuroko goes over thoughts once more, and discovers that Mitori may be hiding in the sewers and that she was led into a trap by Mitori. Mitori's puppet later catches up to Kuroko a ventilation duck. As Kuroko uses another anti-listening device to seal her echolocation, Mitori turns one of the Homing Cameras she has hacked toward the blind spot. Considering the lag when Kuroko teleports and the locations where she is likely to jump to, Mitori has her puppet fire a knife hidden inside it towards Kuroko. However, unbeknownst to her, Kazari has hacked that particular camera to display dummy footage, allowing Kuroko to escape. With this, Mitori then sees Kuroko teleport behind her puppet, the only safespot for her to teleport to, as she predicted. She then sees Kuroko hit by it through the camera, and later has her Homing Camera roll to see Kuroko's body on the floor below. In the sewers, she laughs madly. Mitori apologizes, saying she wouldn't have killed her if she didn't interfere, though she added that she'd still meet the same fate when the city gets destroyed.[31]

Suddenly, Mitori then hears something behind her, and turns to see Kuroko, who has now discovered Mitori hiding in the sewers. Mitori is shocked that her camera, out of the thousands around, had been hacked with dummy footage, to which Kuroko replies that she had the ultimate partner for that. Kuroko then declares that she has nowhere left to run.[31] Cornered and with no time to call her Liquid Shadow, Mitori reaches for her knives, thinking about how she didn't just come down there to hide but also in case she was tracked down, as the passage limited teleportation. She then plans to shoot Kuroko with her ballistic knife when she teleports to avoid her first knife, taking advantage of her lag, taking both of them down if she attacks via teleportation instead. As Kuroko moves forward, Mitori throws the first knife, but to her surprise instead of teleporting Kuroko intercepts it with her hand. Not reacting fast enough, Mitori is then punched then kicked down by Kuroko. Screaming, she lunges at Kuroko with the second knife but Kuroko teleports and kicks her in the back of the head. As she falls in battle, Mitori could only think of Dolly before losing consciousness.[32] Kuroko later handcuffs Mitori intending for her to be taken into custody. Thus, with the help of many people, the destruction of Academy City through the shifting of Misaka Mikoto is averted.

Misaki later uses her power to restore the memories of Kuroko and the others' memories of her, though modified the events somewhat for them, making them believe that they were out trying to catch terrorists targeting the festival to avoid contradictions. Apparently all to hide the existence of both Exterior and the Sisters from public knowledge, as well as passing along the information on the virus to Heaven Canceller to treat the sisters. Mikoto's not participating in the festival events on the second day was changed as well to that of her eating too much and having her stay in the bathroom all day, much to her chagrin.[33]

Now with the waning days of Daihaseisai coming, one night the girls come upon the bonfire where the folk dance is happening, where they note on how they cannot participate. Mikoto goes away to buy them all drinks. In the meanwhile, Kamijou Touma later meets up with Ruiko, and thanks her for the protective charm she lent. Touma offers her to buy her some food to make it up to her, though she says that it is all right. Mikoto later comes around with the drinks, and finds Touma talking with Ruiko. Touma says that he borrowed a protective charm from her, confusing Mikoto though later figures out it was for the borrowing race. Mikoto's stutters and awkward way of presenting herself to Touma does not go unnoticed before the eyes of Ruiko and Kazari.[33]

Capitalizing this new found knowledge, Ruiko approaches Touma and asks him to dance with her around the bonfire as a way to thank her for lending him her protective charm. Touma is fine with the idea, though asks if she is sure with it, to which confirms. Ruiko then tells Touma to go on ahead, leaving the girls alone. Mikoto is utterly shocked by what has transpired, but with a knowing look between Ruiko and Kazari, they make their move. Ruiko fakes an ailment finally catching up to her, prompting Mikoto to ask her if she is okay. However, Kuroko suddenly figures out their ruse and tries to tell Mikoto, but Kazari comes up behind her and covers her mouth. With this ruse finally set up, Ruiko says that she can't move but tells Mikoto that she can dance with Touma in her place. Mikoto becomes embarrassed by this, and makes up a bunch of excuses. Fed up with this, Ruiko forces Mikoto to say that she wants to dance, to which she does.[33]

The girls later see Mikoto dancing with Touma which is unceremoniously interrupted by Kuroko, teleport dropkicking Touma away, much to Kazari and Ruiko's disappointment.[33]

Kuroko enters Sakashima Michibata's salon and tells him to put down his handheld game or else she'll give him some trauma. Kuroko is concerned because Michibata seems unconcerned of getting customers for the salon. Even the staff members that have been only employed there for three months are more worried than Michibata. Regardless, Kuroko goes to a partition and sits down on a chair to get her hair down. Michibata who is unintimated goes to her and removes her hair ribbons to begin his work. Michibata suggests to Kuroko in using new irons he just acquired and asks if she wants a drill or croissant, saying she can be a very domineering. Kuroko doesn't want to, saying that her hair is naturally curly and as such she wants him to give her a straight perm. Michibata asks if it is an afro she wants, to which Kuroko reiterates, by yelling at him, that she wants a straight perm as he puts on the hair dryer helmet on her head.[1]

Afterward as Michibata pulls out a thin pair of scissors, he tells Kuroko that she must have it tough as she is in a prestigious esper school like Tokiwadai and that she needs to get a teacher's permission for the salon she chooses to get her hair cut. He tells that though their school chose him as a designated shop and allowing him to get a lot of easy money, he says that it must be pretty constrained for her having those rules. Kuroko retorts that complaining won't do a thing, saying that it is because people like him can get a basic genetic sample from hair and blood, and as such the school doesn't want someone secretly collecting and mapping someone's DNA. As he continues with Kuroko's hair, he looks above his head the large number of cameras installed by Tokiwadai Middle School. Michibata then says that he has heard a rumor that there is a new subsidy for research on developing teleportation powers as dealing with 11th dimensional coordinates is difficult enough that it is unpopular with the scientists. Kuroko tells him it is not because scientist dislike 11th dimensional calculations, as they most often come up in the quantum theories related to Schrödinger, and says that the higher ups are just worried that there aren't many espers that can teleport. Kuroko says that there are just abilities that show up easily and some that don't. Michibata notes that is one of the mysteries regarding esper powers as he is sure students go through the same Power Curriculum Program but end up with different powers. As he continues to cut Kuroko's hair he wonders why Academy City is even developing powers in the first place, to which she says that he should not deny the very root of Academy City's reason to exist.[1]

Michibata responds that he understands that esper powers are an attractive prospect but says that he thinks that there's some influential person behind it all who dreams of eternal life or world domination. He says to her that he wonders if the text book on esper powers for students like Kuroko even talk about the uproar during the Cold War, referencing the United States and the Soviet Union investing money in it. Kuroko then references the Stargate Project. Kuroko says that they have learned about the project in history class, saying that the scientist had no idea what they were doing and repeatedly kept doing their large-scale experiments despite their inconclusive findings. She concludes that the scientists were just fumbling around and wasting federal funding. Michibata wonders if the project was truly for developing esper powers for military use. He thinks that the project was more for selfish reasons such as being special than for military use. As he continues cutting hair, he then asks if the esper power development between the US and the USSR during the Cold War get their "esper samples". Kuroko says that maybe they were bluffing. Michibata responds that he doubts all of them are fakes, and says that at the very least he doesn't think anyone would wish to create something like an esper without seeing one. Kuroko uses Alchemy as an example, saying that royalty and nobility believed in alchemy because they thought that they had witnessed it with their own eyes, essentially implying that people don't need facts or evidence to believe in something.[1]

Michibata then says that he doesn't believe in superstitious stuff like Alchemy, UFOs, or the New Jersey Devil. Hearing this, Kuroko asks if Michibata is implying that some information on Academy City technology got leaked to the US and the USSR during the Cold War, to which Michibata says that it would be impossible due to the high difference in technology between the outside and Academy City as it would not help them because they did not have the technology to break the advanced encryption. He continues by saying that an "outside" supercomputer in the past wouldn't have been powerful enough to run even the handheld game he is playing, much less crack the encryption and read any information they attained from Academy City. Kuroko then asks what he is implying, to which Michbata asks if she has heard of Gemstones. Kuroko is silent for a moment, and Michibata then asks if he has upsetted her. Kuroko says that he did, saying that her power was brought up by the stimulation of her brain through the Power Curriculum Program, and says that she would rather have him not bring up the term Gemstones. Michibata simply calls it a simple difference between an artificial diamond and a natural one. He says that if a certain phenomenon has been caused artificially, then as long as the same circumstances as in the experiment are recreated in the natural world due to some factor or another, the same phenomenon will occur with no help from humans—basically saying that if espers due to Academy City's curriculum can exist then so do espers in the outside through natural means that are similar to the curriculum. He then compares them as espers being a stun gun and Gemstones being a bolt of lightning. A bored Kuroko denies their existence, saying that Gemstones are just a hypothesis, stating that it is because she has never seen anything like a Gemstone and even if they did then the sample size would be extremely small, a mere error in the data and wouldn't even show up in the total results.[1]

Hearing this, Michibata just smiles and once again challenges her in this debate by using her stun gun and lightning, asking if she thinks lightning strikes rather frequently, to which she says that they do, though extremely rare for it to strike a specific person.[1]

After Uiharu Kazari uses a virtually impossible to crack encryption, the Omega Secret, on the Bank, its server controls, and maintenance tools, in order to prevent a high-level Electromaster intruder from accessing data instead of cutting access to the Bank, Shirai Kuroko goes back to Judgment 177 Branch Office. Here, she tells the bewildered Kazari that she has gone too far and decides to lecture her.[34]

Mikoto and Kuroko are in the shopping district that Index also goes to, leading to a bunch of misunderstandings thanks in part due to Touma’s advice to Index, with Index assuming Mikoto wants Touma’s money and Kuroko becoming suspicious with Mikoto for being violent in back alleys. In the end, a truck passes by before the girls creating a draft, leading to Mikoto and Kuroko’s skirts to be blow upwards.[35]

Seeing this, and the fact that Index has seen a handiwork of a magician in play, Index offers the money to them, to “pay-off” trouble, as Touma advised, much to Mikoto’s chagrin. They of course later decline her offer.[36]

Kuroko, still in a wheelchair from her fight with Awaki, first appears in a family restaurant, and makes a scene there, only to be shocked by Mikoto.

She later reappears with the rest of the gang, accompanying Meigo Arisa as she goes to a photoshoot. She rants about Ladylee Tangleroad not being the real CEO of Orbit Portal Company, and comments on her queer existence. She later, much to her shock, meets Ladylee herself, initially thinking of her as a doll, as she greets Arisa. Kuroko is with her camera as the bombing of the mall they were in begins, and teleports Ruiko and Kazari quickly away. She later returns to the scene of the accident, asking if anyone is hurt, but then discovers that a miracle has happened, and everyone is unscathed.

She later teleports Mikoto towards one of the bridges that leads to Endymion during the climax of the movie, allowing her to destroy a large mobile weapon that prevented Anti-Skill from entering the Endymion, as they have discovered it has been sealed. Mikoto tells Kuroko to stay put as she is still injured. Kuroko is forced to acquiesce as her injuries act up again. She later teleports to Anti-Skill's command post as Kazari discovers that Endymion is about to collapse and they need to destroy the explosive bolts to break it away. Kuroko offers to help Mikoto, but her injury prevents her from doing so. Tsuchimikado Motoharu later contacts them to be a volunteer in destroying one of them, though later has Stiyl Magnus do it instead.

Later, when Anti-Skill is too overwhelmed by Endymion's defenses to even get near one of the explosive bolts, Misaka 10032 contacts them, stating that they will aid it. Kuroko becomes confused as she refers to herself as Misaka, though no more comment is made of this.

Kuroko appears briefly in Ookami-san and her Seven Companions (also produced by JC Staff Animation Studios), smiling mischievously at the audience as a potential bride candidate for the boy millionaire Nezumi Chuutaro. This is, in combination with sharing the same animation studio, a result of Kuroko's voice actor rather blatantly using Kuroko's voice for the part of the series narrator.

In Episode 6 of the second season of the anime Haiyore! Nyaruko-san W, Cthugian Kuuko plans to have a baby with the male main character Mahiro. Trying to combine their both names, Kuuko proposes to name the baby "Kuroko". After that, she says "If it's a girl, we'll enroll her in Academy City."

Her ability is Teleport (空間移動 (テレポート) 能力者,Kūkan Idō (Terepōto) Nōryokusha?, lit. "Space Manipulation User") because of this. Such an ability allows her to teleport herself and anything in her possession a certain distance in the blink of an eye. In volume 8 it is stated that her powers do have limits, being able to transport a total weight of 130.7 kilograms, to a distance of 81.5 meters from herself. It was revealed in Volume 3 of the Toaru Kagaku no Railgun Manga that before she went to Tokiwadai Middle School, she could teleport objects and other people, but not herself. She was eventually able to teleport herself sometime after enrolling in Tokiwadai.

Not only is she able to teleport objects inside designated targets, allowing her to "throw" the darts she carries on her thighs with perfect accuracy, but she can also change their resulting orientation, shown when she teleported a standing Uiharu above a standing Mikoto such that their heads would collide.[37] One disadvantage of her power is that she has to concentrate on where she, the object(s), and/or person she holds will be teleported to, while working out the spatial co-ordinates of jumping between 3-dimensional and 11-dimensional space, so any disturbance in her concentration will render her powers useless, as demonstrated in her fight against Sherry Cromwell. According to Kouzaku Mitori there is a one second lag when consecutively using her power in fights leaving her vulnerable in that one second interval before teleporting again.[31]

Aside from her esper ability, Kuroko mainly relies on the skills she learned from training, which emphasizes throws and take-downs that compensate for her small size. Kuroko specifically focuses on drop kicks. Although usually displayed and used as comedy relief, Kuroko even displays a strong constitution, surviving constantly shocks from Mikoto, having her neck dislocated by the Dorm Supervisor, repeatedly pounding her head on solid objects in fits of either rage or terror or stupidity.

In addition to her darts, Kuroko carries small ball-shaped handheld devices made to interfere with listening devices for security purposes. She uses these to deafen the echolocation of Mitori's Liquid Shadow puppet.[31]

She has been apparently in love with Misaka Mikoto for a long time, whom she calls "Onee-sama" (big sister); when she has the chance she keeps a constant lookout for a chance to get physically intimate with Misaka (getting called a pervert and electroshocked in the process), and tends to get jealous if someone else gets her attention. These attempts have toned down in the manga. Despite her overzealous attempts at gaining Mikoto's favor, her affections appear to be genuine; it has been shown on a few occasions that she is genuinely in love with Mikoto, even allowing herself to get severely injured and hurt in order to help Mikoto. She is regarded as Mikoto's best friend.

There is little change in Kuroko's design. Haimura simply read her description and drew her without any real influence in her design. During her role as the primary heroine in volume 8, Kuroko's design was slightly modified to reflect her importance in the story; It is unclear what changes were exactly implemented.

By volume 12, Kuroko becomes affected by deformed artstyle that Haimura has for the characters. Kuroko was designed with white ribbons for her winter uniform, but this is not brought up in the anime adaptation. According to Haimura, Kuroko was the easiest character to transfer in manga format, for her detailed design for the Toaru Kagaku no Railgun manga.

In episode 15 of the Index anime adaption, during the Angel Fall arc, Shirai Kuroko is depicted to have apparently switched with the US President Barack Obama, using his catchphrase "Yes. We. Can". This was not in the light novels and could be seen as an in-joke for the anime producers, considering Kuroko can also mean "black child" literally in kanji and also because the episode was aired during the US presidential elections.

Satomi Arai's comedic yet thoughtfully mature performance as Kuroko won her the Best Supporting Actress trophy during the Annual Voice Actor Awards in 2010.

Kuroko also has a collection of Misaka Mikoto's pictures that she keeps in an album named "Onee-sama's secret" as shown in Toaru Kagaku no Railgun anime episode 2.

Her spikes are labeled with "Kuroko".

When Kuroko's memories of Misaka Mikoto are erased during the Daihaseisai, Kuroko reacts to Mikoto's close contact, exclaiming, "I'm straight, I swear~!!"[38] This implies that she believed she was straight before she met Mikoto and became infatuated with her.